For almost a decade, starting in 2000, the majority of the Board of Supervisors was split into two camps: progressive liberals aligned with labor and tenants, and the moderates allied with business and pro-development forces. Over the past few years, those distinctions have blurred, and when a new Board of Supervisors convenes in January, they may be all but erased.

It's not that there aren't shades of progressives and moderates left on the 11-member body. But observers expect an overall more centrist tone - at least by San Francisco standards - in which votes are more dictated by individual issues than ideological alliances. That will make the outcomes of big projects before the board next year, including the Golden State Warriors arena and California Pacific Medical Center deal, more difficult to calculate.

"The middle gets bigger ... the board will have more swing, center votes," said Alex Clemens, a lobbyist and longtime City Hall observer. "The increased independence of the Board of Supervisors means that outcomes may be slightly harder to predict. Alliances and allegiances will be focused around an issue of the day, as opposed to a cause of the decade."

The board will welcome two new members Jan. 8 - and probably a third, if Mayor Ed Lee appoints Supervisor Carmen Chu as city assessor, as is widely expected. But it's not just the addition of District Five Supervisor-elect London Breed and District Seven Supervisor-elect Norman Yee that changes the tone of the board, said University of San Francisco political scientist Corey Cook.

He said there has been a gradual shift over the past several years, as the progressive class of 2000 - who rode to victory by painting themselves as the antithesis of then-Mayor Willie Brown and often voted as a bloc - and their moderate counterparts were termed out.

More pragmatic

The replacements on both sides have generally been more pragmatic and willing to reach across the proverbial aisle, Cook said. He said that's been more about a change in personality than ideology - after all, all of San Francisco's supervisors are various shades of Democrats.

"I think the polarization into two camps we experienced from 2000 to more or less 2010 - the fairly clear polarization of moderates and progressives - has largely fallen away," he said. "There's really an increase of pragmatists on both sides. ... The ideology is largely similar to before, but the personalities are different, the skill sets are different and the leadership styles are different."

Two of the biggest changes came in 2008, when District Three Supervisor Aaron Peskin - who had served as board president since 2005 - was termed out; and then in 2010, when the bombastic District Six Supervisor Chris Daly ended his term.

Peskin, a progressive who clashed both professionally and personally with then-Mayor Gavin Newsom, was an outspoken critic of his perceived adversaries and sometimes his allies, and a powerful political organizer who challenged many big real estate developments. He and Daly were known for their aggressive personalities, while their successors - current board President David Chiu and District Six Supervisor Jane Kim - have far more amicable approaches.

It's not just the left wing of San Francisco politics that is changing, personality-wise. Peskin was a master at driving policy debates, Cook said, much as departing Supervisor Sean Elsbernd - who has also been known to forcefully clash with his fellow board members - has been for moderates.

'Changing dynamic'

"It's a changing dynamic on the board - Elsbernd has been a strong pillar of the moderate coalition," Cook said.

The evaporation, or at least weakening, of these voting blocs means that broad issues that have divided the board in the past - including taxes and development projects - are more likely to be decided on a case-by-case basis.

That means, said Clemens, that "conversations may take longer and be more robust."